In motor vehicles such as minivans, sport utility vehicles and the like, it has become common practice to provide the vehicle body with a large rear opening. A liftgate (also referred to as a tailgate) is typically mounted to the vehicle body or chassis with hinges for pivotal movement about a transversely extending axis between an open position and a closed position. Typically, the liftgate may be operated manually or with a power drive mechanism including a reversible electric motor.
During power operation of a vehicle liftgate, the liftgate may unexpectedly encounter an object or obstacle in its path. It is therefore desirable to cease its powered movement in that event to prevent damage to the obstacle and/or to the liftgate by pinching of the obstacle between the liftgate and vehicle body proximate the liftgate hinges.
Obstacle sensors are used in such vehicles to prevent the liftgate from closing if an obstacle (e.g., a person, etc.) is detected as the liftgate closes. Obstacle sensors come in different forms, including non-contact or proximity sensors and contact sensors (e.g., pinch sensors) which rely on physical deformation caused by contact with an obstacle. Non-contact or proximity sensors are typically based on capacitance changes while contact sensors are typically based on resistance changes.
Non-contact sensors typically include a metal strip or wire which is embedded in a plastic or rubber strip which is routed along and adjacent to the periphery of the liftgate. The metal strip or wire and the chassis of the vehicle collectively form the two plates of a sensing capacitor. An obstacle placed between these two plates changes the dielectric constant and thus varies the amount of charge stored by the sensing capacitor over a given period of time. The charge stored by the sensing capacitor is transferred to a reference capacitor in order to detect the presence of the obstacle.
Contact sensors are typically applied in the form of a rubber strip which is routed along and adjacent to the periphery of the liftgate. The rubber strip embeds two wires which are separated by an air gap. When the two wires contact one another, the electrical resistance therebetween drops, and a controller connected to the two wires monitors the drop in resistance, detecting an object when the drop exceeds a predetermined threshold. One problem with such contact sensors, however, is that they have a limited activation angle typically on the order of about thirty five degrees. Thus, in the event the pinch force is applied obliquely rather than head on, the wires may not contact one another.
A need therefore exists for an improved obstacle sensor for use in vehicles and other devices. Accordingly, a solution that addresses, at least in part, the above and other shortcomings is desired.